A. Technical Field
The present invention relates to: a production process for a catalyst for synthesis of an unsaturated aldehyde and/or an unsaturated carboxylic acid; this catalyst; and a production process for the unsaturated aldehyde and/or the unsaturated carboxylic acid by using this catalyst. More particularly, the present invention relates to: a production process for a catalyst for synthesis of an unsaturated aldehyde and/or an unsaturated carboxylic acid, which production process is suitable for producing the catalyst with good reproducibility, wherein the catalyst is excellent in activity, selectivity, and physical strength; a catalyst as obtained by this production process; and a process comprising the step of carrying out catalytic gas phase oxidation of at least one compound selected from the group consisting of propylene, isobutylene, t-butyl alcohol, and methyl t-butyl ether as a raw material with molecular oxygen or a molecular-oxygen-containing gas in the presence of the above catalyst, thereby producing the unsaturated aldehyde and/or the unsaturated carboxylic acid.
B. Background Art
Proposed are a lot of improved catalysts for carrying out catalytic gas phase oxidation of at least one compound selected from the group consisting of propylene, isobutylene, t-butyl alcohol, and methyl t-butyl ether, thereby efficiently producing an unsaturated aldehyde and/or an unsaturated carboxylic acid that correspond to each.
For example, JP-A-013308/1975 and JP-A-047915/1975 disclose catalysts that include Mo, Bi, Fe, Sb, and Ni, and further include at least one element selected from among K, Rb, and Cs as an essential component. JP-A-056634/1989 discloses catalysts that include Mo, Bi, and Fe, and further include at least one element selected from among Ni and Co as an essential component. JP-B-023969/1981 discloses catalysts that include Mo, Bi, and Fe, and further include at least one element selected from IIA and IIB groups as an essential component.
As to the industrial use of the aforementioned catalysts, heat-exchange-type shell-and-tube reactors are generally used. However, the catalysts are packed while being dropped in a reaction tube having a length of several meters to ten and several meters wherein the reaction tube is settled in the above reactor, and therefore it is necessary that the above catalyst should also have sufficient physical strength together in addition to the high activity and the selectivity of the objective product.
In addition, on an industrial scale, catalysts are necessary in large quantities of several tons to dozens of tons, and therefore a person with ordinary skill in the art would sufficiently recognize that: as to a catalyst as produced twice or more, the less the scatter of its activity, selectivity of the objective product, and physical strength is (the better their reproducibility is), the more favorable it is.
From such a point of view, there are also proposed a lot of processes for producing a catalyst with good reproducibility, wherein the catalyst is excellent in activity, selectivity of the objective product, and physical strength.
For example, JP-A-253480/1993 discloses a process that involves carrying out salt decomposition in such a manner that the layer height of not less than 30 weight % of a dried product of catalyst is not lower than 20 mm in a calcination stage. JP-A-238433/1996 discloses a process that involves supporting a catalyst precursor on an inert support, wherein a nitrate radical component and an ammonium radical component are removed from the catalyst precursor by carrying out heat treatment in the temperature range of 200 to 400° C. JP-A-010587/1997 discloses a process that involves carrying out salt decomposition of a dried product as a catalyst precursor by gradually adding it into a flowing gas that is maintained in the temperature range of 200 to 450° C., and thereafter molding and then calcining the resultant decomposed product. JP-A-096162/2001 discloses a process that involves molding and then calcining a powder of a catalyst precursor having an ignition loss ratio of 1 to 5% after the ignition.
The above hitherto proposals (JP-A-253480/1993, JP-A-238433/1996, JP-A-010587/1997, and JP-A-096162/2001) as to the production process for a catalyst all relate to a process that involves removing a salt (e.g. nitrate salts and ammonium salts contained (remaining) in the catalyst precursor) from the catalyst. In these proposals, for example, JP-A-010587/1997 points out that the ammonium salts remaining in the catalyst cause the scatter of chemical and physical properties of the catalyst. In addition, JP-A-096162/2001 points out that the salts and various radical components in the catalyst precursor have an influence on the catalyst performance.
However, there is a problem such that: the catalysts as produced by these hitherto processes have been still insufficient in the activity, the selectivity of the objective product, and the physical strength from the industrial viewpoint, or the reproducibility is lacking for the catalyst production. Therefore, it is desired to further improve the catalysts.